Acetals and ketals are readily obtained by the reaction of aldehyde or ketone hydrocarbons and polyhydroxyl hydrocarbons by many methods well known in the art. There are many references to the efficient preparation of these materials. It is desirable to prepare 2-alkoxy-ethanol compounds, such as 2-n-butoxyethanol and 2-n-propoxyethanol without the requirement of using ethylene oxide as the reactant. It is also desirable to have a process which is robust enough to prepare other hydroxy ether compounds without the requirement of using other highly reactive epoxy compounds and similar materials such as propylene oxide, 1,2-epoxybutane, glycidol (2,3-epoxy-1-propanol) and trimethylene oxide. It is also desirable to prepare hydroxy ether compounds in high selectivity without requiring alkylating agents such as alkyl bromides, chlorides and sulfates in their reaction with polyhydroxyl compounds in a Williamson ether synthesis with the concurrent production of waste salts.
The classes of compounds known as hydroxy ether hydrocarbons have great value as solvents and dispersants for latex paints and other coatings. They also have value as components of industrial and consumer cleaning solutions and surfactants and raw materials for the preparation of polyurethane materials. The large bulk of this class of compounds that are commercially available are generally known as “E-series” and “P-series” solvents. The “E-series” solvents are prepared by the reaction of ethylene oxide (EO) with corresponding alcohols to form the “E-series” products. Conversely, the “P-series” of solvents are prepared by the reaction of propylene oxide (PO) with corresponding alcohols to form similar materials. This technology has a number of concerns and difficulties. First, ethylene oxide and propylene oxide are hazardous materials. Likewise, the nature of the reaction of an alcohol with highly reactive epoxides generates relatively low selectivity for desirable mono addition of EO or PO to the alcohol resulting in di-, tri and poly-EO or PO addition products in significant amounts. Third, the technology of mono ethylene glycol (MEG) production is moving away from the traditional isolation of ethylene oxide and subsequent reaction with water toward more efficient methods to prepare MEG in higher yield that use other technology, such as ethylene carbonate and direct water quenching of crude EO reactor product. These newer technologies remove a ready source of on-site EO for the production of E-series products. Fourthly, historically, a large capital intensive EO/MEG facility needs to be located in close proximity to the alcohol production facility to be efficient and avoid the risk of having to transport EO over long distances. In the case of “P-series” products, a propylene oxide unit also has to be conveniently located. The traditional preparation of PO involves the co-product formation of precursor materials leading to final products such as styrene and MTBE. Other methods to make PO have been developed, as for example, by the use of expensive hydrogen peroxide. The use of PO to make P-series materials thus has cost concerns and secondary co-product environmental concerns.
There is additionally a need to be able to make valuable hydroxy ether hydrocarbons from renewable resources without the need for EO or PO. Much recent work has been carried out to produce ethylene glycol and propylene glycol by the hydrogenolysis of sugars. A large scale process for making MEG and 1,2-propylene glycol (PG) from corn syrup has been commercialized in the People's Republic of China. Ethylene glycol is known to react readily with aldehyde compounds to form, for example, cyclic 2-alkyl-1,3-dioxolane compounds, a class of acetal compounds particularly suitable for the manufacture of hydroxy ether solvents. In a similar manner, 1,2-propylene glycol can form 4-methyl-1,3-dioxolane compounds and 1,3-propylene glycol can form 1,3-dioxane compounds.
Dioxolane compounds are characterized by having a five-membered ring with oxygen atoms in the 1 and 3 positions. Other materials based on renewable materials can also be used to prepare acetal compounds by known reactions with aldehydes, including glycerin, 1,3-propanediol and sugar-derived polyols such as mannitol, erythritol, 1,2- and 2,3-butanediol, and the like. In some of these other examples a class of acetal compound having a six-membered ring with oxygen atoms in the 1 and 3 positions known as 1,3-dioxanes can be prepared. Ketals, may also be prepared by the reaction of ketone hydrocarbons with the above poly hydroxyl hydrocarbons in a similar manner to that of the preparation of acetals.
Previous work has been disclosed in the literature that discusses the hydrogenolysis of acetals, both cyclic and open to produce ether type hydrocarbons. In the case of 1,3-dioxolane acetal compounds, work has been disclosed that describes the preparation of valuable 2-alkoxy ethanol compounds. This chemical transformation is carried out by the cleavage of the oxygen-carbon bond attached to the carbon in the 2-position of the ring with hydrogen using a noble metal catalyst. The focus of that work has been on the liquid-phase hydrogenolysis of acetals in a solvent that is typically the diol moiety used to prepare the cyclic acetal. The art teaches the importance of having a large excess of this diol solvent present during the hydrogenolysis reaction to prevent the formation of significant amounts of undesired co-product, namely a diether.
One example of this reaction is in the preparation of 2-n-butoxyethanol by the palladium catalyzed liquid-phase hydrogenolysis of 2-propyl-1,3-dioxolane in ethylene glycol solvent. A co-product diether compound, namely 1,2-dibutoxyethane, is formed in significant amounts if a large amount of excess ethylene glycol is not used. Diether co-product is particularly undesirable as the formation of one mole of diether consumes two moles of the acetal feed material and at the same time liberates a mole of ethylene glycol. The mole ratio of ethylene glycol to acetal compound has to be greater than 1/1 to produce the desired 2-n-butoxyethanol product in significant amounts. In most of the examples given, a mole ratio of 9/1 EG/acetal is used. This large excess of ethylene glycol solvent creates problems in a practical process by requiring its removal, such as by energy consuming distillation and large equipment required to handle the large volumes created by the use of large volumes of ethylene glycol solvent. Additionally, the use of phosphoric and other similar phosphorous-containing acid co-catalysts and hydroquinone type additives are disclosed as promoters in this process. The same strategy of using excess diol solvent is postulated in the liquid phase hydrogenolysis of acetals where other compounds, such as cyclic acetals prepared from 1,2 and 1,3-propanediol materials and solvents are used, if a favorable selectivity to the desired hydroxy ether product is to be attained. Examples are found in the literature where mixtures of aldehyde and polyhydroxyl hydrocarbons are used directly in a hydrogenolysis process to make the desired hydroxy ether products. In these latter examples, an even higher ratio of polyhydroxyl hydrocarbon/aldehyde is required to effect the desired reaction to prepare the desired hydroxy ether products efficiently. As can be seen from the available art, there is a definite need to be able to carry out the efficient catalytic hydrogenolysis of cyclic acetals to make desired hydroxy ether products, without the use of diol or polyhydroxyl hydrocarbon solvent.